1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to a cooling apparatus of a plasma display panel (PDP) and a method for stabilizing the PDP by minimizing the residual image on the display.
2. Discussion of the Related Art
Generally, a plasma display panel (PDP) has many advantages suitable for the enlargement of various flat board types of display devices.
Due to the above and other reasons, the (PDP) has drawn a lot of attention to enlargement of the panel size.
As shown in FIG. 1, the most typical form of the (PDP) is the one that includes three-electrode and is driven by AC voltage, which is referred to as an AC surface discharge type PTP.
FIG. 1 is a perspective view of the discharge cell structure of a general 3-electrode AC surface discharge type PDP (or AC PDP of surface discharge type having 3-electrode), and FIG. 2 is a sectional view of the PDP discharge cell of FIG. 1.
With reference to FIGS. 1 and 2, the PDP discharge cell includes a pair of sustain electrodes 14, 16 formed on a front substrate 10, and an address electrode 22 formed on a back substrate 12.
On the front substrate 10 on which the sustain electrodes 14, 16 are formed, there are stacked a front dielectric layer 18 and a protective layer 20.
A back dielectric layer 24 and a barrier rib 26 are formed on the back substrate 12 having the address electrode 22 formed thereon, and phosphors 28 are also formed on the surface of the back dielectric layer 24 and the barrier rib 26.
The front substrate 10 and the back substrate 12 are intervald apart from each other in parallel by the barrier rib 26.
Each of the sustain electrodes 14, 16 has a transparent electrode 14A, 16A formed of transparent electrode material (ITO: Indium Tin Oxide) having a high light transmittance, and a metallic subsidiary electrode 14B, 16B which has the narrower width than that of the transparent electrode 14A, 16A, and is formed of metallic material.
As the transparent electrode material (ITO) has a high resistance value, it cannot transfer the power efficiently. Therefore, the metallic subsidiary electrodes 14B, 16B of material (e.g. silver or copper) having a high conductivity are formed on the transparent electrode 14A, 16A to compensate for the resistant component of the transparent electrode 14A, 16A.
The pair of sustain electrodes 14, 16 are driven to function as a scanning/sustain electrode 14 and a common sustain electrode 16.
To the scanning/sustain electrode 14 are supplied a scanning signal for scanning discharge and a sustain signal for maintenance of the discharge.
To the common sustain electrode 16A is mainly supplied a sustain signal.
A wall charge generated during plasma discharge is accumulated on the front dielectric layer 18 and the back dielectric layer 24.
The protective layer 20 raises the discharge efficiency of secondary electrons as well as expands the life span by preventing the damages of the front dielectric layer 18 caused by the sputtering generated during the plasma discharge. The protective layer 20 is normally made of magnesium oxide (MgO).
The address electrode 22 is formed in the perpendicular direction to the pair of sustain electrodes 14, 16.
A data signal is supplied to the address electrode 22 to select the displayed discharge cells.
The barrier rib 26 is formed in parallel with the address electrode 22, and prevents the ultraviolet light and the visible light generated by the discharge from being leaked to the adjacent discharge cell.
The phosphors 28 are excited by the ultraviolet light generated by the plasma discharge, and emit the visible light, for instance, any one of red, green and blue colors.
Inert gas is injected into a discharge space provided between the two substrates 10, 12 and the barrier rib for the gas discharge.
The PDP discharge cell described above is selected by confronting discharge between the address electrode 22 and the scanning/sustain electrode 14, and maintains the discharge by the surface discharge between the scanning/sustain electrode 14 and the common sustain electrode 16, which is a state of sustain discharge.
In the PDP discharge cell, the phosphors 28 emit light by the ultraviolet light generated during the sustain discharge to discharge visible light out of the cell. Accordingly, images are displayed on the PDP. In this case, the PDP controls the discharge duration, i.e. the number of times of sustain discharge according to the video data to realize the gray scale necessary for the image display.
In the 3-electrode AC surface discharge type PDP, the driving duration to express a specific gray level for one frame is divided into a plurality of sub-fields. In each of the sub-field durations, the light emission is generated with the number of times proportional to the weight value of the video data to express the gray level.
A general PDP is driven by an ADS (Address and Display Periode Separated) method wherein one frame is driven with divided into many subfields, each of which has a different discharge frequency to express the gray level of images as above.
For instance, in case of displaying images with 256 gray levels by using 8 bits of video data, the display duration (for instance, 1/60 sec.=about 16.7 msec.) for one frame in each discharge cell is divided into 8 subfields.
Each of the eight subfields is divided into again reset duration, address duration, and sustain duration. The sustain duration of each subfield is provided with a different time weight value at a rate of 2N (here, N is 0, 1, 2, 3, . . . , 7). The time weight value is increased at a rate of 1:2:4:8:16:128 from the first subfield upto the 8th subfield.
As described above, each subfield has a different sustain duration from each other to express the gray levels of images.
The reset duration is the duration to initialize the discharge cell, and the address duration is the duration to generate selective address discharge according to the logical sum of the video data, and the sustain duration is the duration to maintain the discharge in the discharge cell which the address discharge is generated in.
In the PDP, excessive amount of charged particles are generated in the discharge space due to a high voltage or a high temperature.
The phosphors are heated by the collision of the charged particles to leave a residual image on the display screen.
The residual image effect, as shown in FIG. 3, becomes more apparent since a window pattern of a portion 30A of the panel display surface 30 where the discharge is intensively generated to display an image. In other words, the residual image is generated since the window pattern, at a portion on the panel display surface 30 on which, when generating the discharge on the entire surface of the panel, the discharge was intensively generated.
In case of the PDP utilized as a TV or a bulletin board, when displaying a logo of a company or important words by using only a part of the entire surface of the PDP display screen, residual images are generated on the portion on which the logo or the words was located.
In addition, the residual image is seriously shown according to power change, that is, impedance change or surface physical property change of the protective layer 20.
In addition, the main reason that the residual image is generated in the conventional PDP is discharge error of clearance discharge due to the instable driving of the PDP. However, the problem is recently being solved as the clearance discharge is stabilized.
However, there are still many reasons to cause the residual image on the display screen of the PDP in the conventional arts.